Kinetic investigation of Cu(II) ions photoreduction in presence of titanium dioxide and formic acid

Repeated fluctuation of Cu2+ concentration during photocatalytic purification of SMZ-Cu2+ combined pollution: Behavior, mechanism and application

Although the effect of Cu²⁺ on antibiotic removal during photocatalytic reaction has been studied in depth, there is less known about the effect of antibiotics on Cu²⁺ removal. In this study, we report for the first time that, during the photocatalytic purification of sulfamerazine (SMZ) and Cu²⁺ combined pollution, Cu²⁺ concentration showed an obvious five-stage fluctuation, which was completely different from the simple promotion or inhibition reported in previous studies. By employing HPLC-MS analysis and density functional theory (DFT) calculation, the repeated fluctuation of Cu²⁺ concentration was found to be closely related to the SMZ degradation process, mainly resulting from solution pH drop and formation of Cu-containing intermediates which acted as sacrificial agents for Cu²⁺ reduction. In addition, compared with the SMZ-free system, the presence of SMZ can greatly enhance the deep removal of Cu²⁺ (minimum Cu²⁺ concentration was only 0.17 mg/L vs. 1.28 mg/L without SMZ), and there was a wide time interval to ensure the efficient recovery of Cu metal. More interestingly, the in-situ obtained Cu-decorated TiO₂ photocatalyst performed well in water splitting, nitrogen fixation and bacterial sterilization. Results of this study confirmed the great potential of photocatalytic technology in purifying antibiotic-heavy metal combined pollution.

A novel green approach for silver recovery from chloride leaching solutions through photodeposition on zinc oxide

Silver is extensively used in electronics, industrial catalysis, and biomedical sector owing to its enhanced physicochemical properties. E-waste recycling may contribute significantly to enhance silver recovery in the view of a circular economy and limit the depletion of mineral sources. In this scenario, hydrometallurgical routes represent the most widely used techniques for silver extraction/recovery and require strong acidic solutions, high temperatures, and multiple operating units. An alternative sustainable route for silver recovery from leaching solutions used for silver extraction in industrial applications is herein proposed for the first time. The novel green process of silver recovery is based on the UV/vis light-driven photocatalytic deposition of pure metallic silver over low-cost and non-toxic ZnO photocatalyst. In the second step, ZnO is dissolved by slight acidification and pure metallic silver is easily recovered. Low environmental impact, mild operating conditions, and economic viability are among the major perks of the new silver recovery process developed. In the view of a full-scale implementation, several operating conditions of the recovery process (i.e., photocatalyst load, starting silver concentration, type of hole scavenger and irradiation) were thoroughly investigated. A mathematical model capable of describing the system behaviour under different operating conditions was also developed and allowed to estimate unknown kinetic parameters for the Ag-photodeposition process.

Catalysing electrowinning of copper from E-waste: A critical review

Smart technologies and digitalisation have increased the consumption of scarce metals that threaten the sustainability of intricated industries. Additionally, the growing streams of waste electrical and electronic equipment (e-waste) are significant hazards to public health and the environment. Thus, there is an escalating need to recover metals from e-waste for sustainable management of metal resources. Hydrometallurgical processing of e-waste, involving copper (Cu) leaching and its subsequent recovery from pregnant leach solution (PLS) via electrowinning, has emerged as an efficient strategy to close the recycling loop. Electrowinning from PLS demonstrated higher Cu recovery efficiency and operational feasibility with a lower reagent use and lesser waste generation. Nevertheless, multiple issues challenged its practical implementation, including selective recovery of Cu from PLS containing mixed metals and high energy consumption. This review (1) identifies the factors affecting Cu electrowinning from PLS; (2) evaluates the composition of lixiviants influencing Cu electrowinning; (3) appraises various catalysts developed for enhancing Cu electrodeposition; and (4) reviews coupled systems that minimised process energy consumption. From the literature review, electrocatalysts are prospective candidates for improving Cu electrowinning as they reduced the cathodic reduction overpotentials, enhanced surface reaction kinetics and increased current efficiency. Other catalysts, including bioelectrocatalysts and photoelectrocatalysts, are applicable for dilute electrolytes with further investigations required to validate their feasibility. The coupled systems, including slurry electrolysis, bioelectrochemical systems and coupled redox fuel cells, minimise process energy requirements by systematically coupling the cathodic reduction reaction with suitable anodic oxidation reactions having thermodynamically low overpotentials. Among these systems, slurry electrolysis utilising a single-step processing of e-waste is feasible for commericalisation though operational challenges must be addressed to improve its sustainability. The other systems require further studies to improve their scalability. It provides an important direction for energy-efficient Cu electrowinning from PLS, ultimately promoting a circular economy for the scarce metal resources.

Photocatalytic Hydrogen Evolution from Water Splitting Using Core-Shell Structured Cu/ZnS/COF Composites

Hydrogen is considered to be a very efficient and clean fuel since it is a renewable and non-polluting gas with a high energy density; thus, it has drawn much attention as an alternative fuel, in order to alleviate the issue of global warming caused by the excess use of fossil fuels. In this work, a novel Cu/ZnS/COF composite photocatalyst with a core–shell structure was synthesized for photocatalytic hydrogen production via water splitting. The Cu/ZnS/COF microspheres formed by Cu/ZnS crystal aggregation were covered by a microporous thin-film COF with a porous network structure, where COF was also modified by the dual-effective redox sites of C=O and N=N. The photocatalytic hydrogen production results showed that the hydrogen production rate reached 278.4 µmol g⁻¹ h⁻¹, which may be attributed to its special structure, which has a large number of active sites, a more negative conduction band than the reduction of H⁺ to H₂, and the ability to inhibit the recombination of electron–hole pairs. Finally, a possible mechanism was proposed to effectively explain the improved photocatalytic performance of the photocatalytic system. The present work provides a new concept, in order to construct a highly efficient hydrogen production catalyst and broaden the applications of ZnS-based materials.

Photocatalytic selective H2release from formic acid enabled by CO2captured carbon nitride

The selective decomposition of formic acid (FA) traditionally needs to be carried out under high temperature with the noble metal-based catalysts. Meanwhile, it also encounters a separation of H₂and CO₂for pure H₂production. The photocatalytic FA dehydrogenation under mild conditions can meet a growing demand for sustainable H₂generation. Here, we reported a photocatalytic selective H₂release from FA decomposition at low temperature for pure H₂production by Pt/g-C₃N₄. Low-cost and easy-to-obtained urea was utilized to produce carbon nitride as the metal-free semiconductor photocatalyst, along with a photodeposition to obtain Pt/g-C₃N₄. The electrochemical evidences clearly demonstrate the photocatalytic activity of Pt/g-C₃N₄to produce H₂and CO₂in one-step FA decomposition. And, the impedance is the lowest under simulated solar light of 70 mW cm^-2with a faster electron transfer kinetic. Under simulated solar light, H₂production rate is up to 1.59 mmol · h^-1· g^-1for FA with concentration at 2.65 mol l^-1, 1700 000 times larger than that under visible light and 1928 times under ultraviolet (UV) light. DFT calculations further elucidate that nitrogen (N) active site at the g-C₃N₄has an excellent adsorption towards CO₂molecule capture. Then, H₂molecules are selectively released to simultaneously separate H₂and CO₂in solution. Platinum (Pt) at Pt/g-C₃N₄as the catalytic site contributes into the acceleration of H₂production.

A Study on Photo-Fenton Method for Simulatenous and Synergic Decreasing Concentration of Pb(II) and Cu(II) in the Solution

To prevent an environmental pollution by hazardous heavy metals, in the present study, a simulatenous decrease of the concentration of Pb((II) and Cu(II) in the solution by photo-Fenton method has been systematically studied. Photo-Fenton process proceeded in a close reactor by batch technique. The process was conducted by exposure solutions containing Pb(II) and Cu(II) ions, and Fenton’s reagent (Fe2+ and H2O2) under UV-A lamp. In this study, the initial concentations of Pb(II) and Cu(II), and the exposure time were optimized. The synergyc effect that may be appeared on the decrease of Pb(II) and Cu(II) ion concentrations simultaneously through photo-Fenton process was also addressed. The concentrations of Pb(II) and Cu(II) in the solution were determined by AAS. The research results exhibited that photo-Fenton process could decrease Pb(II) and Cu(II) concentrations, and the maximum decreases, 46.12 % dan 16.86% for Pb(II) and for Cu(II) respecticely, were found by applying both initial concentration of Pb(II) and Cu(II) as much 35 mg/L, and 60 min of the time. The concentration decreases of Pb (II) and Cu(II) were results of oxidation by OH and by electron to form PbO2 and Cu particles respectively as probed by EDX data. Furthermore, photo-Fenton process toward a solution containing Pb(II) and Cu(II) ions allowed oxidation of Pb(II) and reduction of Cu(II) simultaneously and showed a synergic effect. Such effect was demonstrated by the fact that the presence of Cu(II) ion in the photo-Fenton process of Pb(II) solution could improve the Pb(II) oxidation and the highest improvement of Pb(II) oxidation (81.06%) was shown by 35 mg/L of the Cu(II) concentration. Similarly, the presence of Pb(II) in the photo-Fenton process of Cu(II) solution could enhance the reduction of Cu(II), and the highest effect on the Cu(II) reduction enhancement was exhibited by 35 mg/L of the Pb(II) concentration.

Efficient Photocatalytic Reduction of Aqueous Perrhenate and Pertechnetate

The pertechnetate anion (⁹⁹TcO₄^-) is a long-lived radioactive species that is soluble in aqueous solution, in contrast to sparingly soluble ⁹⁹TcO₂. Results are reported for photocatalytic reduction and removal of perrhenate (ReO₄^-), a nonradioactive surrogate for ⁹⁹TcO₄^-, using a TiO₂ (P25) nanoparticle suspension in formic acid under UV-visible irradiation. Re(VII) removal up to 98% was achieved at pH = 3 under air or N₂. The proposed mechanism is Re(VII)/Re(IV) reduction mediated by reducing radicals (^·CO₂^-) from oxidation of formic acid, not direct reduction by photogenerated electrons of TiO₂. Recycling results indicate that photocatalytic reduction of ReO₄^- exhibits excellent regeneration and high activity with >95% removal even after five cycles. ⁹⁹Tc(VII) is more easily reduced than Re(VII) in the presence of NO₃^- with very slow redissolution of reduced ⁹⁹Tc. This study presents a novel method for the removal of ReO₄^-/⁹⁹TcO₄^- from aqueous solution, with potential application for deep geological disposal.

CFD modeling of a UV-A LED baffled flat-plate photoreactor for environment applications: a mining wastewater case

The use of ultraviolet light in photoreactors for wastewater treatment has become popular as an alternative of known chemical oxidative substances. UV LED light represents cheaper, robust, and versatile alternative to traditional UV lamps. In this study, it was designed and evaluated a photoreactor with an approach of chemical fluid dynamics (CFD) and experimental validation. The evaluation consisted of (1) CFD velocity profile analysis, (2) characterization of the average light distribution with potassium ferrioxalate actinometry, (3) degradation of a typical recalcitrant metallic cyanocomplex Fe(CN)₆^3-, and (4) scavenger effect analysis in the photodegradation using potassium persulfate. Actinometrical essay concluded that the system was able to receive 1.93 μE/s. The reactor operated under turbulent regime and best result for Fe(CN)₆^3- degradation was obtained at 4 h of operation, using 5-W UV-A LEDs, with pH ~ 7 and 10 mM de S₂O₈^2-. Baffled photoreactor demonstrated to be useful for this type of illumination and wastewater treatment.

Anoxic photocatalytic treatment of synthetic mining wastewater using TiO2and scavengers for complexed cyanide recovery

A new pathway for selective photocatalytic reduction using a combination of scavengers for gold mining wastewater treatment.

Assessment of TiO2 photoactivity on the lead removal: kinetic and mechanistic processing

Removal of lead ions from aqueous solutions, in the presence and in absence of commercial TiO₂, under UV-light was studied. The influence of catalyst mass, concentration of Pb(II) ions and of citric acid in the starting solution as well as the impact of illumination conditions on the removal rate were also investigated. The results were fitted on the pseudo-first order, pseudo-second order and Elovich kinetic models, Weber-Morris intraparticle and liquid film diffusion models, in order to establish the photoreduction mechanism. The Pb removal rate increased in time by a combined linear-exponential mechanism. The catalyst had a positive influence on the removal rate at the start of the photoreduction. At a low concentration of Pb(II) ions (20 mg/L), the amount of photoreduced Pb(II) ions was proportional to the concentration of the citric acid solution, but at high concentrations (240 mg/L), the correlation was inversely proportional. The rate limiting steps in the removal of lead were both the photoreduction on the TiO₂ surface and the diffusion through the film surrounding the catalyst particle. The lead removal was significantly influenced by the mobility and by the concentration of the species in solution.

Cleaning of olive mill wastewaters by visible light activated carbon doped titanium dioxide

Visible light activated carbon doped titanium dioxide fully works in the removal of total phenols from olive mill wastewater.

Growth behaviour and plasmon resonance properties of photocatalytically deposited Cu nanoparticles

Cu nanoparticles (NPs) were deposited on UV-irradiated TiO(2) in an aqueous solution containing Cu(CH(3)COO)(2) and ethanol by a photocatalytic reaction. Cu NPs on TiO(2) exhibit an extinction (= absorption + scattering + reflection) peak due to localized surface plasmon resonance at around 600 nm initially. The density and size as well as the extinction of Cu NPs increase during the deposition, accompanied by a slight redshift of the peak. Eventually, TiO(2) is mostly covered with coalesced Cu NPs that exhibit a spectrum less characteristic of Cu NPs, but more characteristic of a Cu layer.

Energy recovery in wastewater decontamination: simultaneous photocatalytic oxidation of an organic substrate and electricity generation

The contemporary removal of organic pollutants from aqueous solution and electricity generation is studied in the present work by means of an experimental device resulting from the combination of a photocatalytic reactor and an electrochemical cell. The proposed system relies on the capability of Cu2+ ions to reduce in the presence of TiO2, (solar) UV radiations and a sacrificial organic agent. In the anodic solution of the combined photoreactor-cell, Cu0 is oxidized to Cu2+ and the latter is reduced again to the lowest oxidation state. The use of different sacrificial agents ranging from formic acid (FA) to glycerol (GLY) to glucose (GLU) is investigated along with the adoption of two different cathodes for the cell, the first based again on the couple Cu2+/Cu0 and the second on the couple O2/H2O.